12 SOME STEM TUMOES OK KNOTS OIT APPLE AND QUINCE TREES. 



from crown-gall, is in the opinion of the writer only a form of the 

 same disease as woolly-knot and these aerial tumors. The simple 

 form of hairy-root occurs most frequently upon seedling trees: it is 

 present both on the stem and root portions of the trees. It consists, 

 when it occurs on the roots, of numerous fine roots growing at right 



angles from the 

 main roots or the 

 taproot (fig. 10). 

 These side roots 

 are very soft and 

 succulent at first, 

 but later harden 

 and have a wiry 

 appearance and 

 texture. On the 

 roots they are 

 usually quite uni- 

 formly distributed 

 in definite belts. 

 Where this form 

 occurs on shoots it 

 springs more fre- 

 quently from the 

 vicinity of a bud 

 (fig. 11), of ten just 

 beneath it. These 

 fine roots are 

 formed in groups, 

 or bunches, a 

 great many often 

 springing from a 

 single origin. 

 The origin of each of these clumps of roots is similar to that of the 

 rudimentary roots in the aerial tumors. It follows, then, that the 

 hair^'-root disease may have at least three forms, which are more or 

 less distinct : The simple, the woolly-knot, and the aerial forms. 



EFFECT OF THE DISEASE UPON TREES. 



Owing to the complexity in the forms of the hairy-root disease 

 and the difficulty of obtaining accurate information as to their final 

 effect upon orchard trees, and in view of the fact that extensive ex- 

 j)eriments are being conducted to determine the nature of each form 

 and its effect upon the life and fruitfulness of apple trees, it will not 

 be safe at present to make a definite statement as to the effect of these 

 tumors further than to give the observations of the writer. 



[Cir. 3] 



Fig. 9.- 



-The woolly-knot form of hairy-root on a Northern Spy 

 apple tree grown in an experiment. 



